I don't know the word επιεικτης and can't find it in LSJ Perseus. I don't remember ever seeing ιει like that. But it looks like τὰ ἄλλα some kind of accusative compliment to the adjective: ...another son, on the one hand capable of the other things, (but) on the other hand dumb.

But that word is pretty annoying. Can you check it and add the accents?

Could also be adverbial, but that seems more for decrees than people: capable for the rest but dumb